The present invention belongs to the field of locking nuts wherein a nut is locked upon a threaded member engaged in the nut threaded bore as a result of local deformation of a portion of the threaded bore wall, once the nut has been threaded in position on the threaded member.
The prior art is replete with lock nuts provided with a locally deformed thread or a locally deformed threaded bore resulting in a predetermined amount of interference fit between the nut thread and the thread of a male member on which the nut is threaded. Such lock nuts, sometimes called prevalent torque lock nuts, require that a substantial torque be applied to the nut for threading it upon the threaded member. In the prior art, lock nut structures are also found which comprises a deformable soft metal, or plastic, annular or longitudinal insert in the nut threaded bore, so as to provide a substantial amount of frictional interference between the nut internal thread and the external thread of the threaded member engaged in the threaded bore. Such prior art lock nut structures present the disadvantages of requiring additional torquing, sometimes of an excessive amount, for threading the nut on the threaded member, and causing substantial deformation of the threaded member. The limited amount of frictional resistance to relative motion between the nut and the threaded member achieved by such structures is substantially decreased as a result of repeated disassemblies of the elements which cause rapid wear and damages to the nut itself and to the threaded member engaged therewith. The end result is decreased locking capability as a result of torque loss due to wear of the soft metal or plastic inserts in the nut threaded bore.
Other nut locking devices are also found in the prior art, such as provided by a conventional nut and a counternut torqued in firm engagement with each other, by a tongued washer whose tongues are bent over after the nut has been torqued into position so as to engage a flat portion of the outer periphery of the nut body for immobilizing it into position, by the drilling of a cross hole through the nut body and the male threaded member and locking of the nut into position by means of a cotter pin or wire, or even by the use of permanent assemblies wherein the nut is welded or soldered to the threaded male member after torquing of the nut in position.
Other prior art nut locking means may consist of threaded bores radially disposed in the nut body, each provided with a set screw having an end driven in engagement with the threaded member periphery after the nut has been torqued into position. Such an arrangement may obviously damage the thread of the threaded member to the point that disassembly of the elements may be prevented.
Further, locking nut structures are found in the prior art, such as those disclosed in Brogren, Swedish Pat. No. 50020 or Pollard, British Pat. No. 871,405, which require a groove intersecting the threaded bore portion in order to create the locking feature. A set screw is therein used to deform the locking element so as to contact the threaded member located in the locking nut. Torquing of the set screw not only creates highly localized holding forces, but causes the locking element to act as a threading die, thereby cutting into the threaded male member when locked into position into the nut. Further, the distribution of the locking force is such that the highest concentration is at one end of the locking element where at the opposite end of the locking element there is virtually no locking force. It is because of this nonuniform distribution of locking force that these types of locking nuts tend to act as threading dies when threaded upon a male member.
Prior art such as those mentioned, as well as Berto, Norwegian Pat. No. 70883, have the disadvantages of creating highly localized locking forces thereby causing damage to the threads of the male member upon which the locking nut is threaded. Further, the nonuniform distribution of the locking force along the axis of the threaded bore results in a substantially lower holding force thereby requiring excessive deformation of the locking element which over a period of time will result in damage to the threads of the threaded male member.